1. Field of the Invention
This invention pertains to the general field of equipment used to lift people confined to wheelchairs in order to help them function normally within the constraints provided by appliances and apparatus designed without regard to the special requirements resulting from their disabilities. In particular, it provides a new and improved way of lifting a wheelchair to a variable height for use either as an adjustable chair or as a means for ramping to a higher elevation.
2. Description of the Prior Art
Although various designs of wheelchairs have been in use for centuries, only during the last couple of decades a serious effort has been made to accommodate the needs of disabled people and give them an equal opportunity to function normally in our society. As part of that effort, public facilities have been required to remove obstacles to the unhindered movement of wheelchairs on streets, sidewalks, and in buildings. The result has been a welcome change in the standard construction of these facilities to include ramps and similar structures to make it possible for people in wheelchairs to go places without unnecessary hardship.
Because of the room requirements involved in the placement of permanent ramps, which can be prohibitive for a high rise because of the low climbing grade needed to maintain easy and safe access, various devices have been developed to perform the same function within a more confined space. In principle, they all consist of means for lifting an occupied wheelchair from a lower to a higher level for specific applications. For example, U.S. Pat. No. 4,576,539 to Williams (1986) describes a wheelchair lifting device to provide access to public transit vehicles. It consists of a platform for supporting the wheelchair; a frame along which the platform is raised and lowered; and a chain/gear/sprocket system with driving means to elevate the platform. A hydraulic jack is used to position the frame, while the chain/gear/sprocket system is used to lift the platform for simplicity and smoothness of operation.
In U.S. Pat. No. 4,158,524 (1979), Serafin teaches a chair lift designed to provide access to buildings in general. It consists of a platform fixed to frame legs capable of pivoting around a stationary base. The platform is elevated as the legs move progressively from a horizontal to a vertical position. The legs are driven by a cable/spool system actuated by an electric motor.
U.S. Pat. No. 4,674,601 to Benjamin (1987) describes a stationary apparatus to gain access to an elevated doorway in a building. This invention consists of a canvas shoot anchored to rigid beams capable of pivoting around the door's threshold. The beams are driven by cables spooled from the upper portion of the door. Conceptually different in all respects from the present invention, the function of this apparatus is limited to providing access to and from a particular door.
U.S. Pat. No. 4,365,692 to Craig (1982) shows a lifting device similar to the apparatus disclosed by Serafin. It consists of a catwalk attached to legs anchored to a base and capable of pivoting from the horizontal to the vertical position, thus causing the rising of the catwalk. The disclosure is limited to drilling site applications and designed to provide a higher floor level for operations around the well bore.
U.S. Pat. No. 3,888,463 to O'Brien (1975) teaches a wheelchair lifting apparatus specifically designed for portability and variable lifting range. It comprises a platform elevated by hydraulic rams driven by a battery powered mechanism. The rams operate on lever arms that move the wheelchair platform to the desired elevation. Through a complicated lever system, the platform is maintained in a horizontal position during travel from ground to an elevated level.
In U.S. Pat. No. 4,457,402 (1984), Del Vecchio shows a stationary lift that combines traditional stairs and a wheelchair lifting platform for dual use. The platform hoist is an expandable scissor-lever assembly driven by a hydraulically activated piston rod.
U.S. Pat. No. 4,790,716 to McConnell teaches an apparatus to lift and position a wheelchair to allow for the provision of specialized services to its occupant, such as dental and similar work. The lifting device is based on scissor-type levers driven by a worm-screw/chain/gear mechanism and a reversible motor. The inventive portion of this patent lies mainly in the specialized applications made possible by its use.
Finally, U.S. Pat. No. 2,661,927 to Hulsart (1953) discloses a general weight hoist for any suitable application. It describes a platform lifted on scissor-type levers driven by a continuous screw mechanism. The invention does not describe the use of rams to lift the platform and it does not address any application involving wheelchairs.
The main problem with the lifts and related equipment described above is that they involve complicated structures that are bulky and expensive, resulting in uneconomical application for the purposes intended here. They provide an alternative to ramps in order to move from one level to another, but they do not provide a means to adjustably position the elevation of a wheelchair to an efficient height for the task at hand. In addition, these machines tend to be slow in operation and inefficient for the job of raising the elevation of a relatively light load. Thus, they are not suitable for use in situations where the occupant may need or wish to change the elevation of the wheelchair frequently and promptly, such as at spectator events in theaters and arenas. Therefore, there still exists a need for a simpler, self-operated device for positioning a wheelchair at variable heights in order to enable a user either to perform otherwise uncomfortable duties in stationary fashion or to lift the wheelchair to a higher level for locomotion. It is the purpose of this invention to address these problems.